Together the foot and ankle have over 25 bones and 33 joints along with more than 100 named muscles, tendons, and ligaments and a network of blood vessels, nerves, all residing beneath a relatively slim covering of soft tissue and skin. Structurally, the foot has three main anatomical regions: the forefoot, the midfoot, and the hindfoot. These parts work together with the ankle, to provide the body with support, balance, and mobility. A structural flaw or malfunction in any one part can result in the development of problems, which are manifested in other areas of the body.
The forefoot includes the five toes (which are also known as the “phalanges”) and their connecting long bones (or “metatarsals”). Several small bones together comprise a phalanx or toe. Four of the five toes have three phalanx bones respectively connected by two joints. The big toe (or “hallux”) has two phalanx bones distal and proximal with a joint in between called the interphalangeal joint. The big toe articulates with the head of the first metatarsal at the first metatarsophalangeal joint (the “MTP” joint) and there are two tiny, round bones called sesamoids on the plantar side of the metatarsal head. The phalanges are connected to the metatarsals at the ball of the foot. The forefoot balances pressure on the ball of the foot and bears a substantial amount of the body weight.
The bones of the midfoot from medial to lateral are the 1st through 3rd cuneiform, the cuboid, and the crescent shaped navicular bone posterior to the cuneiforms, which also forms a joint with the talus that forms the basis for the ankle joint at the hinged intersection of the tibia, the fibula, and the foot The five tarsal bones of the midfoot act together form a lateral arch and a longitudinal arch which help to absorb shock. The plantar fascia (arch ligament) underlays the bones of the midfoot and along with muscles, forms a connection between the forefoot and the hindfoot. The toes and their associated midfoot bones form the first through fifth rays beginning with the great toe as the first ray.
The hindfoot is composed of three joints (subtalar, calcaneocuboid & talonavicular) and links the midfoot to the ankle. The heel bone (or “calcaneus”) projects posteriorly to the talus and forms a lever arm to activate the hinged action of the foot so as to allow propulsion of the entire body from this joint. The calcaneus is joined to the talus at the subtalar joint.
The mid-foot is often the subject of trauma such as results from falls, vehicle crashes and dropped objects. These accidents often result in severe fractures and/or dislocations. A common midfoot fracture is the Lisfranc injury which was identified by a French doctor in the Napoleonic Wars. It commonly occurred when a cavalier fell from his horse with his foot caught in his stirrup and resulted in the fracture and dislocation of multiple bones of the midfoot. A Lisfranc injury has come to indicate an injury to the normal alignment of the cuneiforms and metatarsal joints with the loss of their normal spatial relationships. These types of injuries may occur from dropping a heavy object on the top of the foot or stepping on an uneven surface and falling with the foot in a twisted position. These fractures also occur in athletes when the foot is bound to an article of sports equipment such as skis or snowboards or when the foot is subject to simultaneous impact and rotation, such as skating or ballet jumps or soccer.
A common Lisfranc injury occurs at the joint primarily involving the 1st and 2nd metatarsals and the medial cuneiform. Normal alignment of the joints is lost if the ligaments are disrupted and the bones separate between the medial and mid-cuneiforms or between the 1st, 2nd metatarsal and the medial cuneiform. Failure to treat such an injury may result in joint degeneration and subsequent damage to the adjacent nerves and blood vessels.
Typical surgical treatment of the midfoot re-establishes the normal anatomy of the mid-foot while the fractured bones mend. In some cases, fusion of the joint between the first and second metatarsals and the middle and/or internal cuneiforms may be necessary, for example, where arthritis arises in patients with a prior Lisfranc or similar injury. One current surgical treatment of this injury requires that pins, wires and/or screws be inserted to stabilize the bones and joints and hold them in place until healing is complete. For example, a pin or screw may be introduced medially into the internal cuneiform and through the base of the second metatarsal bone. While the use of k-wires, pins, and screws may provide acceptable results for younger and more plastic patients, these methods of fixation are not always satisfactory.